Fuel tank safety caps are often provided, and are required in certain applications, to cover the fuel tank of gasoline or diesel powered vehicles or machinery. The caps must provide a secure closure for a filler neck or the like of a fuel tank, but must be readily openable, but lockable, as desired. In addition, a cap should include an automatic pressure relief mechanism to prevent pressure buildup within a fuel tank due to temperature rise of the fuel, or other factors. As fuel in the tank is consumed during operation of the vehicle or machinery, an increasing vacuum can develop within the tank which can impair operation of the engine by preventing efficient fuel flow.
Accordingly, it is desirable to provide both vacuum and pressure relief to prevent such occurrences. Further, as time goes on, additional environmental regulations, safety requirements and other regulatory restraints are placed on this type of equipment. Thus, it would be desirable to accommodate ongoing design modifications into existing equipment, without requiring the substantial costs associated with new castings and molds, for example.